A typical method for effectively controlling a safety system is shown in German Published Patent Application No. DE-OS 38 03 426. During an accident, the forward displacement of a vehicle occupant is calculated using the signal from an accelerometer. If the forward displacement of an occupant, derived through computation, exceeds a specified value, a safety device (such as an inflatable air bag) is activated. A disadvantage of this system is that the criterion for the tripping action is based on a fictitious occupant position. The fictitious occupant position may not necessarily conform to the actual sitting position of the occupant, thus decreasing the accuracy in the control of the safety device.
Another known system for motor vehicles, which includes the use of an inflatable protective impact cushion, is disclosed in German Published Patent Application No. DE-OS 38 09 074. In accordance with this known system, the sitting position (center of gravity) of the driver is determined through the use of pressure sensors arranged on the track of the motor vehicle seat. Based on the information from the pressure sensors, the protective impact cushion is only partially inflated when the vehicle occupant is positioned in a location relatively close to the front of the motor vehicle.
Another known method is disclosed in German Patent Application No. DE-P 37 43 059.9 which proposes using measurement techniques to detect the actual sitting position of a motor vehicle occupant. Such measurements are obtained through the use of a suitable sensor, such as an ultrasonic transmitting receiver or a passive infrared sensor. Based on the detected sitting position of the occupants, particularly the position of the passenger, the decision to fully or only partially inflate an inflatable air bag, provided for the passenger, is made. The determination to activate the safety means is based on the measured limiting acceleration value. This method does not use the sitting position of the motor vehicle occupant as part of the tripping criterion for the safety means. Rather, the sitting position is used only to determine if the safety means are to be partially or fully inflated.
It is an object of the present invention, therefore, to overcome the problems of known methods and apparatus for protecting motor vehicle occupants.